The present invention relates to a pumping plant for installations carrying water, comprising a split-tube motor and a rotary pump driven by the same, the impeller of which is situated on the shaft extremity present within the pump space, which is carried by two radial anti-friction bearings situated at either side of the rotor stack of laminations, said shaft consisting of ceramic material at least in the area of these anti-friction bearings and is longitudinally movable with respect to the ceramic bearing rings of the radial anti-friction bearings under forces acting axially on the impeller, the maximum length x of this longitudinal displacement being limited by two axial anti-friction bearings.
Depending on its source and place or origin, the water from the conventional water supply mains contains greater or lesser proportions of admixtures which may lead to corrosion or calcification of the plant. Breakdowns of the pumping plant are caused less by corrosion than primarily by calcareous deposits commonly caused by calcium hydrocarbonate (Ca(HCO.sub.3).sub.2) which when the water is heated precipitates as insoluble calcium carbonate CaCO.sub.3 and forms the so-called boiler scale.
This calcium carbonate also settles as a coating on the periphery of the pump shaft so that the coating is drawn into the radial anti-friction bearings carrying the shaft during axial movements of the shaft, which frequently results in seizing of the shaft. Moreover, longitudinally directed displacement movements of the shaft are unavoidable in the case of faucet water installations. For example, they are caused by sudden opening of water cocks since the forces caused thereby act in surging manner on the pump impeller and displace the same axially together with the shaft, that is from a position decisive for the case of stationary or static operation into a non-stationary position from which the shaft finally returns automatically to the initial position after termination of the energy pulse.
The axial freedom of the shaft between the two positions is rendered possible moreover by the production technique applied in each instance and in particular also by the axial compressibility of the resilient seals, and last but not least is also needed to avoid excessive stress on the shaft. The maximum length of the axial shaft displacement is however determined and limited in finite manner by two axial bearings.
Under the given circumstances, no possibility is thus available in this case of simply precluding the previously referred to risk of shaft seizure simply by preventing any axial freedom of the shaft, so that in the case of the arrangements hitherto known, it had always had to be expected that deposits or coatings present on the shaft periphery would be pulled into the radial bearings during an axial shaft displacement.
It is an object of the invention to provide an uncomplicated as well as economical solution to this problem, consisting in the manner in which a shaft seizure in the radial anti-friction bearings may be precluded despite the unavoidable deposits on the shaft periphery.